Cantileverlike device in fluid-mechanical alarm

ABSTRACT

In fluid operated instrumentation of process and/or energy control, a flexibly supported cantileverlike diaphragm unit as a high sensitivity device which lends itself to miniaturization and integrated fluid systems; further, in such instrumentation, wherein mechanical movement devices exemplified by diaphragms, force-bars, and baffles for fluid nozzles are combined with fluid circuitry, and wherein design is in the nature of miniaturization and integrated fluid systems, a dynamic system plate in which different portions are flexible and separate movement devices, as exemplified above, and which may include cantileverlike structures whereby the plate includes movement devices of a system or subsystem, as a dynamic integrated system plate; and further, in such instrumentation, an alarm system operable through change in the restriction of a nozzle upon the application of a signal to a nozzle-baffle assembly, one example of such an alarm system including a simple cantilever, or a dynamic plate with a cantilever and a force arm as parts of the plate. Passive elements, such as pneumatic restrictors, may also be embodied in the plate.

United States Patent 72] Inventor Philip H. Sanford Walpole, Mass. [2!]Appl. No 772,595 [22] Filed Nov. 1, 1968 [45] Patented Apr. 6, 1971 [73Assignee The Foxboro Company Foxboro, Mass.

[54] CANTILEVER-LIKE DEVICE IN FLUID- MECHANICAL ALARM 6 Claims, 25Drawing Figs.

[52] US. Cl 340/240, 200/81 [51] Int. Cl I-I0lr 11/26 [50] Field ofSearch 340/240; 200/8 1 .2, 81.3

[56] References Cited UNITED STATES PATENTS 3,374,323 3/1968 Peek340/240X Primary Examiner-Ralph D. Blakeslee Attorney-Lawrence H. PoetonABSTRACT: In fluid operated instrumentation of process and/or energycontrol, a flexibly supported cantileverlike diaphragm unit as a highsensitivity device which lends itself to miniaturization and integratedfluid systems; further, in such instrumentation, wherein mechanicalmovement devices ex emplified by diaphragms, force-bars, and baffles forfluid nozzles are combined with fluid circuitry, and wherein design isin the nature of miniaturization and integrated fluid systems, a dynamicsystem plate in which different portions are flexible and separatemovement devices, as exemplified above, and which may includecantileverlike structures whereby the plate includes movement devices ofa system or subsystem, as a dynamic integrated system plate; andfurther, in such instrumentation, an alarm system operable throughchange in the restriction of a nozzle upon the application of a signalto a nozzle-baffle assembly, one example of such an alarm systemincluding a simple cantilever, or a dynamic plate with a cantilever anda force arm as parts of the plate. Passive elements,

' such as pneumatic restrictors, may also be embodied in the plate.

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PHILIP H. SANF'ORI) CANTILEVER-LIKE DEVICE IN FLUID-MECHANICAL ALARMThis invention relates to process and/or energy control instrumentationof the fluid operated type having fluid systems which operate in part byapplying forces to movement parts, in a fluid mechanical combination.Such movement parts are various in their nature and use and may be madequite small, for example, to lend themselves to ultimate miniaturizationin terms of a size allowing several such devices to be integrated with atotal size of an ordinary postage stamp or less.

Such movement parts, especially when there are several in a system,ordinarily require considerable space, and often substantial fluid forceand/or volume.

The modern need in such instrumentation is for miniaturization andcircuit integration. Fluidics, like electronics, has been developed inthis direction with various advantageous forms of circuit boards forfluid passages in miniaturized and integrated designs and structures.

This invention provides a concept in aid of this effort in that itprovides miniaturization and integration techniques and structure,particularly for the moving parts of a fluid-mechanical system, whileproviding in small space the gain and stroke factors of previous largerand separate devices.

An example of this invention is a thin, flexible metal plate with anintegral cantilever structure formed therein. One use of this cantileveris as a high sensitivity, long stroke diaphragm unit, taking up butlittle space, and formed by covering the flexible metal plate with asheet which may be formed of elastic, such as rubber, so that thecantilever is a flexibly supported arm mounted on and essentiallysurrounded by rubber. A stiffener for the cantilever may be used wheredesired. Thus, pressure on one side of this combination will produce along bending movement of the cantilever followed by the surroundingrubber. Very sensitive short stroke devices can similarly be formed.

A cantilever structure in a thin, flexible metal plate can be used toproduce a force-strip, cantilever mounted somewhere along its length ina sensitive, light weight and small version of a force-bar structure inthe much larger and heavier control unit devices of the prior art. Thisstructure can also produce a very useful, high sensitivity, long strokediaphragm unit, and also may be stiffened as desired.

Various movement devices may be built into the thin metal plate, forexample, by etching away metal around the desired forms or devices.Metal diaphragm areas of usual and unusual diaphragm shapes and formsmay be integrally formed in the thin metal plate. For example, a capsulewith a portion of the flexible plate as a movable end, can take theplace of a bellows. Spring rates, gain and stroke considerations may bebuilt in or provided by local area treatment, as desired.

This invention provides a dynamic integrated plate in which moving partsof a particular system, or subsystem, may be incorporated in a singlethin metal plate, a considerable advance for miniaturization andintegrated structure in instrumentation control systems offluid-mechanical combinations. This plate structure lends itself to theuse of a sandwich unit in which the plate is sandwiched with a fluidcircuit board, with the passages needed to service the mechanics of theplate located within the circuit board.

This invention further provides an alarm system wherein a nozzle-baffleassembly is operated to vary the nozzle-baffle restriction in responseto an alarm signal, usually a fluid pressure applied to the baffle. In asmall, compact assembly of such an alarm system, one structure includesa dynamic movement plate wherein the baffle is a cantilever structure asdescribed hereinbefore. Other movement structures may be used in such analarm assembly flexible plate, such as a forcearm, and a flexible-endcapsule, to the end that an alarm system may be provided, in the natureof a miniaturized, integrated dynamic plate device wherein moving partsare incorporated in a thin flexible metal plate. Passive elements suchas pneumatic restrictors may also be embodied in the plate.

Other objects and advantages of this invention will be in part apparentand in part pointed out hereinafter and in the accompanying drawings,wherein:

FIGS. 1 through 6 are various views of a simple cantilever diaphragmunit according to this invention;

FIGS. 7 and 8 are top view and central section views respectively, of acantilever unit according to this invention, with housing backingformation in support of the molded or elastic body in the cantileverdiaphragm unit;

FIGS. 9 and 10 are, respectively, plan and edge views of a dynamic plateincluding, by way of example, simple cantilevers and a force-armcantilever, by way of illustrating the integrated dynamic plate conceptof this invention, in the nature of miniaturization of fluid systems inprocess and/or energy instrumentation; passive pneumatic restrictors arealso shown;

FIG. 11 is a schematic illustration of a nozzle-baffle alarm systemconcept according to this invention;

FIG. 12 is an illustration of an alarm system in further explanation ofthe concept of FIG. 11;

FIG. 13 shows physical locations on the dynamic plate of the elementsshown schematically in FIG. 12;

FIG. 14 is a vertical lengthwise section through an alarm structureembodying the system of FIGS. 11 and 12;

FIGS. 15, 16, 17 and 18 are, respectively, top, side, sideview section,and right end views of the structure of FIG. 14, in terms of theposition of FIG. 15;

FIG. 19 is an illustration of a reed switch operational system accordingto the alarm structure of this invention with a specific showing ofdiaphragm structure;

FIG. 19A is a lengthwise section through the structure of FIG. 19;

FIG. 20 illustrates an alternative form of the device of FIGS. 11 and12;

FIG. 21 illustrates an alternative system for alarm on rateof-processchange;

FIG. 22 is an alternative to the system of FIG. 20, as an alarmacknowledge device;

FIG. 23 is an alternative to FIG. 12, utilizing an electricalsnap-switch; and

FIG. 24 is a further variant of the structure of FIG. 12.

CANTILEVER DIAPHRAGM Diaphragm devices are in common use in fluidinstrumentation. They are devices which are fully peripherallysupported, capable of having only relatively short stroke and lowsensitivity, and they take up substantial space. This invention, in thenature of miniaturization and system integration, provides a diaphragmunit which may be of any shape, supported in a way to produce adiaphragm with long stroke, high sensitivity capability in small space.It is based ideally on a cantilever support to achieve the mostsensitivity and highest stroke but variations on this mounting may beused.

Accordingly, as illustrated, this invention provides a new and usefulconcept, based on cantilever diaphragm units. They are useful in anydiaphragm application, particularly in miniaturization and integratedsystems. The cantilever support concept may use a single cantileversupport or in special cases, several cantileverlike supports. They canbe used as force-balance or motion diaphragms in a variety ofminiaturized applications in fluid-mechanical systems. The cantileverforms may be achieved by etching, stamping, or other suitable processfrom materials such as thin beryllium copper, stainless steel, or othersuitable materials, one example being glass. These devices have theadvantages of metal diaphragms combined with the advantages of simpleelastic dividing walls.

A simple cantilever is formed by removing material of a horseshoe form.The surrounding material is fixed, leaving the tongue free to move. Thedevice may be backed up by a sheet of rubber cemented on the pressureside to form a pressure barrier.

in FIG. 1, a cantilever plate 10 is provided with a cutout cantileverarm 11, which may be pivotable about its base, on

line 12. In FIG. 2, the edge view shows the cantilever arm 11 in theplane of the plate 10, and in FIG. 3, the cantilever arm II as bent outat an angle from the plate 10, illustrating its long stroke capability.In FIG. 4 the simple showing is of the backup rubber sheet 13 moldedwith the deflected shape of FIG. 3.

In FIGS. 5 and 6 respectively, the rubber sheet I3 is shown assandwiched with the plate 10, with the rubber sheet 13 and thecantilever arm 11 extended, and in simple alignment.

In FIGS. 7 and 8, a simple cantilever diaphragm unit is shown, wherein afluid signal input passage 14 leads to a pres sure chamber 15, on therubber side of the diaphragm unit. Pressure in the chamber 15 raises thecantilever arm 11. Further, the cantilever arm is provided with astiffener plate 16, and an upper housing 17 is provided with a backupwall 18, to support the rubber sheet 13 as it is deflected by themovement of the cantilever arm, to leave a minimum area of the sheetfree and open to the actuating pressure. The contour of the backup wall18 is designed to maximize flexibility and stroke. The pressure thusincreases as the stroke lengthens, to a point of maximum support of therubber.

The rubber sheet 13 may be an elastic, stretchable body, or it may be aslack body of rubber or other suitably extendablc material, for example,various fabrics may be used. Their purpose is to move with thecantilever and to provide fluid seal condition around the cantilever, towhatever controlled degree is desirable for the particular application.

DYNAMIC SYSTEM PLATE AS INTEGRATED MOVEMENT PLATE The necessary trend ofmodem instrumentation has been toward miniaturization while maintainingand improving system integrity, dependability and repeatability, in theface of increased requirements as to performance and complexity. Thepneumatic field has developed useful circuit boards to this end and forsuch purposes.

This invention presents a new and useful step in this area by providinga dynamic system integrated plate for the mechanical movement devicesassociated in and with fluid instrument systems. Pure fluid devices,with no moving parts, have their important place in this art, but moreoften it is found that a practical combination of pure fluid devices andsome moving parts is most desirable.

This invention provides a dynamic system plate in which moving parts ofsuch a system are located in a thin metal sheet, with each elementestablished in a different portion of such a sheet in suitable form andflexibility for its particular purpose. As an example, such elements canbe in cantilever form, in various cantilever shapes or combinations.Thus, any moving part of an instrument system may be built into such adynamic plate in one form or another, with whatever associated elements,such as stiffeners, as may be desired. Many high sensitivity pneumaticcomponents may be combined on a single small sheet of spring materialsuch as thin stainless steel for such an integrated pneumatic component,In addition it is possible to include in this integration, springs,force bars, and any other mechanical elements which may lend themselvesto this concept of design. Restrictor openings may also be providedthrough such a sheet.

An example of application of a dynamic system integrated movement plateis provided hereinafter with respect to the alarm system presented as anembodiment of this invention.

In FIGS. 9 and 10, to illustrate the dynamic system, such a movementsystem plate is shown at 19, with rubber backing sheet 20. This platecontains a group of simple cantilever diaphragm units in two differentsizes at 21 and 22, with the smaller cantilever having pivot areacutouts as at 23, to reduce the spring rateof those particular elements,and a single forcearm cantilever at 24. This system plate is applicableto the alarm system exemplified later herein as an embodiment of thisinvention. Many other such plates may readily be formed for otherdesired applications, in great complexity and variety, in the nature ofconcentrating all the moving parts of an in strument or a subsystem ofan instrument in a single, thin sheet. Various shapes and functions maythus be so incorporatedv While this concept springs from the cantileverconstruction, other movement constructions can similarly be incorporatedas needed for particular applications. For example, various springformations may be locally incorporated in different areas ofthcintegrated sheet.

ALARM ACTUATOR SYSTEM AND STRUCTURE WITH CANTILEVER EXAMPLE Alarmsystems are vital and necessary adjuncts to instrumentation systems,Especially in modern high volume processes and expensive energy systemsthe cost of uncontrolled or wrongly controlled conditions or parameterscan be very large. Instant and reliable alarm systems are essential.

Since they are an adjunct to an operations system, their size andcompatibility with the operations systems are matters of real concem.

In this invention, simple nozzle-baffle alarm systems are presented, andwhere miniaturization and system integration needs are involved, thedynamic system plate of this invention fills the needs, and can be basedon the cantilever diaphragm concept of this invention. All of the switchdiaphragms, inverter diaphragms and the like in the actuator systems areincorporated in the integrated system plate of FIG. 9, in itsapplication to the structure of FIG. I4 through 18.

The alarm actuator of this invention provides an accurate, adaptable,pneumatically actuated alarm unit for use with controllers, recorders,indicators and auxiliary stations. Integrally actuated 24-volt AC alarmlights with or without an external signal for rclay'operation can beprovided. The basic actuator, with minor changes, is capable ofproviding the following alarm functions (not shown):

Absolute Alarmthe alarm is a function of an absolute value in themeasurement span of the instrument. Whenever the measurement reacheseither an adjustable high level or a separately adjustable low level,lights may be activated and a signal for external 24-volt AC relayactuation may be provided.

Deviation Alarm-The alarm is a function of difference between controllerset point and measurement. The deviation alarm actuator provides twoindependent adjustments which permit the operation of alarm lights at apredetermined deviation of the measurement above and below the controlpoint, or above or below the set point. A common signal is provided toactuate a common external relay if desired. More than one suchcombination may be used for different applications.

In order to avoid switch flutter" where the measurement contains randomnoise variations, the unit may be equipped with adjustable dead bands.

The operating principle of the actuator is illustrated in FIG. 11. Themeasurement pressure is introduced into a bellows 40 which drives aflapper bar 41. The flapper bar also rests upon two air nozzlesdesignated high alarm and low alarm. Above the bar at the high alarmnozzle is a spring 42 having adjustable compression, and above the barat the low nozzle is a second spring 43 having adjustable compression.This constitutes a force-balance system whereby an increase inmeasurement may overcome the compression spring, causing the flapper barto pivot on the low nozzle, venting the high nozzle to the atmosphere.Conversely, a decrease in measurement, with the aid of the tensionspring, will cause the flapper bar to pivot on the high nozzle, to ventto the low nozzle. Thus, the pressure in the bellows vs the adjustmentof the springs determines the point at which each nozzle will open.

For example, suppose the springs are adjusted so that with 9 p.s.i. inthe bellows, both nozzles are covered, the compression spring could beadjusted so that the high nozzle would vent at psi. and the tensionspring could be set so that the low nozzle would vent 8 p.s.i. By usingthe vented nozzle to initiate an alarm signal, duplex alarm action isprovided. By adjusting one of the springs so that the nozzle beneath itdoes not vent within the 3 l 5 psi. span of measurement pressure, singlehigh or low alarm signals can be accomplished.

FIG. 12 illustrates how the venting of the nozzles maybe used to producean alarm signal and provide a means for adjusting dead band (also knownas lockup). It also indicates the difference between the deviation andabsolute alarm units. As drawn, it is a schematic for a duplex deviationalarm. The force at the bellows end of the flapper is due to anydifference between the pressures in the measurement and set bellows.Once set to function at specific values above and below the set-point,alarm actuation will occur whenever the measurement and set-pointpressures deviate by the preset values.

By removing the set bellows, the unit becomes an absolute alarm. Theonly force at the bellows end of the flapper bar is now due to thepressure in the measuring bellows. The high and low alarms, once set,will now be representative of absolute points in the span of measurementand remain fixed.

In FIG. 12, trace a high alarm signal through the circuit. The highnozzle 44 is connected to the diaphragm chamber of a spring-adjusted airswitch 45 and receives its air supply through restrictors 46 and 47. Thehigh alarm nozzle 44 being open, the spring 48 of the air switch willlift the diaphragm 49 and its attached magnetic shunt 50. The magnet nowcloses the reed switch 51, actuating the alarm light 52. The air switchspring 48 may be made adjustable. No air is consumed except during alarmconditions.

At the same time the alarm signal is actuated, a connection betweenrestrictors 46 and 47 permits pressure from the upper diaphragm chamberof a pneumatic signal inverter 54 to bleed off through restrictor 47 andthe high alarm nozzle 44. An air supply 55 to the lower inverter chamber56 lifts the diaphragm 57 from the inverter nozzle 58 permitting air toflow from chamber 56 through restrictor 59 to the positive feedbackcapsule diaphragm 60. The line to this capsule is vented through anadjustable restrictor 61. Pressure, and thus force in the positivefeedback capsule 60 is a function of the difference in resistancebetween restrictors 59 and 6]. Force applied by the feedback capsule 60opposes the effect of the compression spring 62 and must be overcome bypressure drop in the measurement bellows before the high alarm nozzle 44can close. This provides a dead band adjustable from a minimum of theorder of l percent; of measured span to a maximum of the order of 8percent. The positive feedback capsule is located to produce the samedead band on either alarm point.

A single output actuator differs from FIG. 12 in that a connection 64 ismade between the high and low nozzles 44 and 63, and one of the inverterand pressure switch circuits is omitted, providing only one outputsignal. Since the springs are adjustable over 100 percent of span, thissignal may be made to represent high alarm only, low alarm only, orcommon high and low alarm using the same alann device.

This unit provides optional basic alarm functions plus combinations:high accuracy; repeatability of the order of gpen cent; high and lowalarm adjustable over I00 percent measured span; deviation alarmadjustable 1100 percent: adjusta ble dead band lockup. The feature thatno air is consumed except during alarm conditions is apparent since bothnozzles are ordinarily closed by the baffle arm 65. Since the drop inair pressure in the nozzle circuits actuate the alarm, the device isfail-safe in the event of leakage or air failure.

Actual structure of the system of FIG. 12, utilizing the principles andoperation of FIG. 11, based on the cantilever diaphragm unit and dynamicsystem plate concepts hereinbefore described, as in FIGS. 13 through19A, is shown with like reference numbers applied to like elements asfrom FIG. 12. Note in FIG. 13, pneumatic restrictor openings indicatedas R.

In the remaining FIGS. through 24, various alternative alann actuatorsystems are set forth schematically. Actual structure for these systemsis similar to that of FIGS. 14

through I9A, and similarly lends itself to the use of cantileverdiaphragm units and integrated system plates as described hereinbefore.

FIG. 20 illustrates a high-low alarm with avariable switch differentialor dead band. In this version the typical nozzle restrictor is replacedby a variable pressure divider 66. When one of the nozzles is open by analarm condition a portion of the drop across the restrictor appears as adrop in the smaller bellows 67 opposite the nozzles. This results in avariable snap action or dead band which may be adjusted as a function ofthe setting of the variable pneumatic potentiometer.

In some instances it would be desirable to monitor the measurementsignal and produce an alarm when the process changes at an excessiverate. Shown in FIG. 21 is a deviation type of alarm modified by pipingthe measurement pressure through an adjustable restrictor 69 to thebellows normally used for the set point pressure. This will produce analarm signal whenever the measurement changes faster than apredetermined rate.

FIG. 22 illustrates a high-low similar to that shown in FIG. 20. In thissystem however, the small bellows used for dead band is replaced by abellows 70 large enough to generate a snap action which is capable ofpercent dead band resulting in a system which must be acknowledged aftereach alarm. Acknowledgement is accomplished by repressurizing the snapaction bellows 70. This may be accomplished by mechanically depressing areset bellows 71 connected to the bellows 70.

A further modification is illustrated in FIG. 23. This is a simpledevice using a microswitch 72 to obtain an alarm directly. Dead band isfixed at the value provided by the switch.

FIG. 24 illustrates another way of accomplishing similar alarm systems,like FIG. II except the measurement signal is applied to the baffle armbetween the nozzles.

This invention therefore provides new and useful movement means influid-mechanical instrumentation in the nature of miniaturization andintegrated fluid systems.

As many embodiments may be made in the above invention, and as changesmay be made in the embodiment set forth above without departing from thescope of the invention, it is to be understood that all matterhereinbefore set forth and in the accompanying drawings is to beinterpreted as illustrative only and not in a limiting sense.

Iclaim:

I. A fluid operated alarm system comprising; a battle arm, a pair ofnozzles disposed along said baffle arm, each such nozzle being arrangedto apply a fluid jet to said baffle arm, resilient means biasing saidbaffle arm restrictively against said nozzles, and means for applying asignal force to said baffle arm in one direction to significantly closeone of said nozzles and significantly open the other of said nozzles,and in another direction to significantly open said one of said nozzlesand significantly close said other of said nozzles, with the consequenceof alarm operating changes in pressure in each of said nozzles.

2. An alarm system according to claim I wherein said nozzles are both onthe same side of said baffle, and said resilient biasing means comprisesindividual and adjustable springs, one disposed oppositely of saidbaffle at the location of each of said nozzles, said means for applyinga signal force to said baffle arm comprising bellows means adjacent oneend of said arm.

3. An alarm system according to claim I wherein a fluid supply line isprovided to at least one of said nozzles, a pressure divider restrictoris located in said supply line, a deadband bellows is applied to saidbaffle arm, and a fluid connection is provided between a tap connectionof said pressure divider and said dead-band bellows.

4. An alarm system according to claim 3 wherein said deadband bellows isrelatively large and capable of 100 percent dead-band snap action, and areset bellows is connected to said fluid connection from said pressuredivider as an alarm acknowledge device.

5. An alarm system according to claim 1 wherein said means for applyinga signal force to said baffle arm comprises a measurement bellows on oneside of said baffle arm, a set-point bellows on the other side of saidbaffle arm, a fluid rate connection between said measurement andset-point bellows.

6, An air operated alarm system for use in industrial instrumentation asa device for responding to an air signal as a measurement representationof variation of a value of a parameter beyond a predetermined norm, saidsystem comprising:

A support base, a baffle arm mounted on said base in cantilever fashion,a high alarm nozzle mounted on said base to direct an air jet to theunder side of said baffle arm adjacent one end of said arm, a positivefeedback capsule diaphragm mounted on said base for force engagementwith the under side of said baffle arm at an intermediate point alongthe length of said arm, a low alarm noule mounted on said base to directan airjet to the under side of said baffle arm at a point beyond saidcapsule diaphragm from said high alarm nozzle, a set pressure bellowsmounted on said base and in force engagement with the under side of theother end of said baffle arm;

support top plate, a measurement bellows mounted dependingly from saidtop plate and in force engagement with the top of said baffle arm and inopposition to said set bellows, and a spring adjustably mountedeffectively on said top plate and against the top of said baffle arm inopposition to said low alarm nozzle and another spring in like mountingin opposition to said high alarm nozzle;

an air supply connection to said high alarm nozzle through one pair ofrcstrictors in series, an air supply connection to said low alarm nozzlethrough another pair of restrictors in series, a signal outputconnection from each of said air supply connections from a point betweensaid restrictors and their respective nozzles;

a signal inverter for said high alarm nozzle, comprising a housing, adiaphragm dividing said housing into two chambers, an inverter nozzleinto one of said chambers and restrictable by said diaphragm, a springin the other of said chambers biasing said diaphragm restrictablyagainst said inverter nozzle, an air supply connection to said nozzlechamber, an air connection between said spring chamber and said highalarm air supply at a point between the restrictors thereof,

a like signal inverter for said low alarm nozzle, a common airconnection to said capsule diaphragm, an air connection from each ofsaid inverter nozzles through individual restrictors to said commonconnection, and a variable restrictor bleed to atmosphere from saidcommon con nection. I

1. A fluid operated alarm system comprising; a baffle arm, a pair ofnozzles disposed along said baffle arm, each such nozzle being arrangedto apply a fluid jet to said baffle arm, resilient means biasing saidbaffle arm restrictively against said nozzles, and means for applying asignal force to said baffle arm in one direction to significantly closeone of said nozzles and significantly open the other of said nozzles,and in another direction to significantly open said one of said nozzlesand significantly close said other of said nozzles, with the consequenceof alarm operating changes in pressure in each of said nozzles.
 2. Analarm system according to claim 1 wherein said nozzles are both on thesame side of said baffle, and said resilient biasing means comprisesindividual and adjustable springs, one disposed oppositely of saidbaffle at the location of each of said nozzles, said means for applyinga signal force to said baffle arm comprising bellows means adjacent oneend of said arm.
 3. An alarm system according to claim 1 wherein a fluidsupply line is provided to at least one of said nozzles, a pressuredivider restrictor is located in said supply line, a dead-band bellowsis applied to said baffle arm, and a fluid connection is providedbetween a tap connection of said pressure divider and said dead-bandbellows.
 4. An alarm system according to claim 3 wherein said dead-bandbellows is relatively large and capable of 100 percent dead-band snapaction, and a reset bellows is connected to said fluid connection fromsaid pressure divider as an alarm acknowledge device.
 5. An alarm systemaccording to claim 1 wherein said means for applying a signal force tosaid baffle arm comprises a measurement bellows on one side of saidbaffle arm, a set-point bellows on the other side of said baffle arm, afluid rate connection between said measurement and set-point bellows. 6.An air operated alarm system for use in industrial instrumentation as adevice for responding to an air signal as a measurement representationof variation of a value of a parameter beyond a predetermined norm, saidsystem comprising: A support base, a baffle arm mounted on said base incantilever fashion, a high alarm nozzle mounted on said base to directan air jet to the under side of said baffle arm adjacent one end of saidarm, a positive feedback capsule diaphragm mounted on said base forforce engagement with the under side of said baffle arm at anintermediate point along the length of said arm, a low alarm nozzlemounted on said base to direct an air jet to the under side of saidbaffle arm at a point beyond said capsule diaphragm from said high alarmnozzle, a set pressure bellows mounted on said base and in forceengagement with the under side of the other end of said baffle arm; asupport top plate, a measurement bellows mounted dependingly from saidtop plate and in force engagement with the top of said baffle arm and inopposition to said set bellows, and a spring adjustably mountedeffectively on said top plate and against the top of said baffle arm inopposition to said low alarm nozzle and another spring in like mountingin opposition to said high alarm nozzle; an air supply connection tosaid high alarm nozzle through one pair of restrictors in series, an airsupply connection to said low alarm nozzle through another pair ofrestrictors in series, a signal output connection from each of said airsupply connections from a point between said restrictors and tHeirrespective nozzles; a signal inverter for said high alarm nozzle,comprising a housing, a diaphragm dividing said housing into twochambers, an inverter nozzle into one of said chambers and restrictableby said diaphragm, a spring in the other of said chambers biasing saiddiaphragm restrictably against said inverter nozzle, an air supplyconnection to said nozzle chamber, an air connection between said springchamber and said high alarm air supply at a point between therestrictors thereof; a like signal inverter for said low alarm nozzle, acommon air connection to said capsule diaphragm, an air connection fromeach of said inverter nozzles through individual restrictors to saidcommon connection, and a variable restrictor bleed to atmosphere fromsaid common connection.